1. Field of the Invention
The invention relates to a process for the preparation of alloy powders. These alloys are based on titanium and can be sintered. They are prepared by the calciothermal reduction of the oxides of the metals which form the alloys in the presence of inert additives.
2. Description of the Prior Art
Because of their special properties, titanium and alloys based on titanium are very useful. However, due to the relatively costly manufacturing processes, titanium and especially alloys of titanium, are relatively expensive.
In the manufacture of titanium, the naturally occurring oxide is reduced with carbon in the presence of chlorine to produce titanium tetrachloride. This is reduced with metallic sodium or magnesium to titanium sponge. After the addition of further alloying components, such as, for example, aluminum and vanadium, the titanium sponge is then fused and cast or rolled into rods, shapes or sheets. The shaped parts having approximately the desired contour, are converted to their final form by machining. This mode of operation is advantageous since it produces considerable amounts of alloy cuttings. Consequently, it is not possible to economically produce parts having a complicated shape unless extra steps are taken, which increase the cost.
Manufacturing parts having such shapes is more successful using the powder metallurgy method. Two processes in particular have become known for the preparation of alloy powders. One process involves fusing the titanium sponge together with the alloying partners into a rod-shaped electrode. The electrode is dispersed to a powder by rotating at high rates of revolution under a plasma flame. However, because of the formation of agglomerates, the powder obtained must usually be subjected to an additional comminution or milling. This so-called "REP" process is exceptionally expensive, primarily due to the equipment cost. Also, it is limited, relative to the charge weight, to a particular size of electrode.
The second known method for the preparation of the powder consists of hydrogenation of the titanium sponge, milling the brittle titanium hydride, mixing it with the remaining alloying components in powder form, intimate milling, dehydrogenating at elevated temperatures under vacuum and molding and sintering the powder obtained by conventional procedures. This method is also expensive and is disadvantageous from a process engineering point of view.
German patent No. 935,456 discloses a process for the production of alloy powders suitable for the manufacture of sintered parts, by the reduction of metal compounds, and, if necessary, subsequently dissolving out the by-products. This process is characterized by the fact that intimate mixtures of such metal compounds, one of which at least is difficult to reduce, are reduced with metals, such as, sodium or calcium. In one embodiment of the process, the reduction takes place in the presence of inert, refractory, easily leachable materials.
This patent describes the co-reduction of oxides of titanium, copper and tungsten as well as of other oxides. The process has not been put into practice because it does not produce powders which can be sintered and which are homogeneous in regard to their composition and structure.